The present invention relates to a power transfer system for motor vehicles and, in particular, to a drop box having means for establishing an angular driving connection between its input and the output of a multi-speed transmission.
In view of the increased popularity of sport utility vehicles, a plethora of power transfer systems are currently utilized for delivering tractive power (i.e., drive torque) to the driven wheels of the motor vehicle. Conventionally, most two-wheel drive power transfer systems for rear wheel drive vehicles include a rear prop shaft which connects the output shaft of the transmission to the rear axle assembly for driving the rear wheels.
However, a problem commonly associated with this type of power transfer system is that the rear prop shaft, due to its central alignment, takes up a substantial amount of the vehicle's underbody space which inhibits placement of an underbody spare tire and/or necessitates usage of a saddle-type gas tank. To alleviate this problem, it is known to install a transfer device, commonly referred to in the industry as a "drop box", between the transmission output shaft and the rear prop shaft. Typically, the drop box has an input shaft coupled to the transmission output shaft, an output shaft laterally offset from the input shaft, and a drive connection (i.e., layshaft, chain drive, etc.) interconnecting the output shaft for driven rotation with the input shaft. Accordingly, utilization of a drop box provides increased underbody space for purposes of locating a spare tire and/or installing a larger fuel tank.
A design consideration associated with vehicles equipped with a drop box is to minimize the departure angle at the rotary connection between the drop box output shaft and the prop shaft. The departure angle is defined as the included angle between the rotary axis of the prop shaft and the rotary axis of the drop box output shaft. Traditionally, single cardan universal joints are used at each end of the prop shaft if the departure angle is less than about five degrees. If the departure angle exceed this threshold limit, then more expensive double cardan universal joints are typically required at the prop shaft/drop box connection. In an attempt to solve problems similar to those associated with large departure angles for drop boxes, U.S. Pat. Nos. 4,632,207 to Moore and 5,116,293 to Reuter disclose the use of a constant velocity (CV) joint at the offset front output of a four-wheel drive transfer case. An alternative arrangement is likewise shown in U.S. Pat. No. 4,688,447 to Dick. However, in each instance, the rear output of the transfer case is commonly aligned with the rotary axis of the transfer case input.